Cables, such as electric wires that are at risk of shaking and vibration and to being exposed to moisture and drenching with liquid, are usually laid in corrugated flexible protective tubing. A previously known practice in this respect is to provide some form of spacing means as protection against wear caused by rubbing between the cables and the inside wall of the tubing. An example is found in WO 2000-36614. The spacing means according to this publication takes the form of expansible foam material that is expanded to at least partly fill the space in the tubing. Foam material is mechanically sensitive and highly flexible in response to powerful stresses.